The present invention relates to a method for using excess heat of flue gas that is not required for operating a flue gas desulfurization device, the flue gas being introduced into an air preheater and an electrostatic filter before entering the desulfurization device.
The present invention further relates to a device for using excess heat of flue gas not required for operating the flue gas desulfurization device, the device having an air preheater and an electrostatic filter upstream of the desulfurization device.
In known power plants provided with a flue gas desulfurization device the combustion air which is introduced into the steam generator is first guided through an air preheater in order to improve the degree of efficiency of the power plant, whereby the air preheater is heated by the flue gas exiting from the steam generator. The thus cooled flue gas is usually scrubbed by an electrostatic filter before being introduced into the flue gas desulfurization device. The desulfurized flue gas is then released into the atmosphere via a flue gas smoke stack or a cooling tower. The release of the scrubbed flue gas via a cooling tower is advantageous because the flue gas which has been cooled during the scrubbing process within the desulfurization device and has been laden with moisture may be released into the atmosphere without requiring a directed reheating of the flue gas.
In power plants with steam generators that are primarily fueled with fossil fuels a great flue gas volume relative to the volume of combustion air is produced. With brown coal power plants this ratio is approximately 1.6 to 1. Since for the prevention of corrosion a certain difference between the exhaust gas temperature and the acid due point must be observed, the flue gas temperature after leaving the electrostatic filter is approximately 170.degree. C. for such power plants.
Since on the other hand the required temperature for the flue gas desulfurization process is approximately 110.degree. C., in known power plants the temperature of flue gas before entering the flue gas desulfurization device is reduced from 170.degree. C. to approximately 110.degree. C. by injecting water. However, this results in a loss of efficiency of approximately 3% occurs. For a brown coal power plant with an electric power output of 800 MW, i.e., a thermal power output of approximately 2400 MW, the aforementioned loss of efficiency due to reduction of the excess heat by injecting water into the flue gas is thus approximately 80 MW of thermal efficiency, i.e., approximately 3% of the total efficiency of the brown coal power plant.
It is therefore an object of the present invention to provide a method and a device of the aforementioned kind with which the excess heat not needed for the operation of the flue gas desulfurization device may be utilized.